1. Field of the Disclosure
The present invention relates to an improved internal combustion engine which can be operated in a four-stroke pneumatic modes according to the preamble of annexed patent claims.
2. Related Art
A plethora of suggestions and patents have been made in more than 100 years development to increase the overall efficiency of internal combustion engines as e.g. used in vehicles.
A rather old general concept for increasing the efficiency of an engine driven vehicle is directed to the recuperation of vehicle brake energy otherwise lost in friction brakes. This can be done by using the engine as a compressor, storing the compressed air inside a pressure vessel. This then enables to use the compressed air for pneumatic propulsion of the engine, either in connection with a normal thermal mode, i.e. when burning fuel, or without burning fuel, the so-called pneumatic mode (or air motor mode). This configuration is achieved by connecting one or more combustion chambers (i.e. cylinders) by the means of variable actuated valves to the pressure vessel. A further advantage of such a system consists in the ability to pneumatically restart the engine after stop.
The pneumatic modes can be achieved using one engine revolution (2 strokes). However, for such an operation not only the valves for the pressure vessel need to be fully variable in their actuation but also the inlet and exhaust valves of the combustion engine must fulfil the same criteria. The fully variable valves result in a very expensive and not reliable construction which is far away from today's production facility and proved technology. Since for normal thermal operation, a high variability of intake and exhaust valves is not necessary, this solution is more complex than necessary.
U.S. Pat. No. 3,958,900 was filed in the name of Takahiro Ueno and published in 1976. The document describes a fully mechanical combined engine and air compressor apparatus, whereby an engine action and an air compression action are changed over to each other by changing valve timing of inlet and exhaust valves in a purely mechanical manner. To achieve the for the operation necessary flexibility in valve timing and valve control a very complex mechanism with three adjustable cam shafts is foreseen to control the opening of the valves. Based on the information available the engine has never been commercially successful.
WO04106713A1, assigned to Lotus Cars Limited, is directed to an internal combustion engine with a combustion chamber which is connected to a reservoir for storing compressed air. Electro hydraulic valves which control the gas flow are arranged between the chamber and the reservoir so that air pressurised in the chamber can be relayed to charge the reservoir and pressurised air can be delivered to the chamber to drive piston. The chamber is also used for combustion of fuel. The disclosure also relates to a valve mechanism for controlling the flow of pressurised air between the chamber and reservoir. The valve mechanism applies a balancing force to the gas flow control valve to cancel the force on the valve arising from the pressure applied to the back face of the valve. Not only the charge valve but also the inlet and exhaust valve are actuated in a electro hydraulic manner.
WO05079418 (also published under US2006/0052930), of Froloff et al., discloses a dynamically re-configurable multi-stroke internal combustion engine, comprised of programmable computer processor controlled engine components for decoupling the four classic strokes of an internal combustion engine and electronically managing engine cylinder components including such cylinder components as electronically controllable valves, fuel injection and air fuel mixture ignition, allowing additional engine cylinder unit component states and thus cylinder strokes to be independently altered or re-sequenced by computer control to provide alternate engine modes of operation. Alternate engine modes are facilitated by addition of a compressed air storage reservoir to receive compressed air generated by the cylinder. In a further mode compressed air is transferred to the cylinder units to increase engine power and efficiency or utility. The described devices have a very complex Sensor input and on-demand requirements drive control logic to manage engine strokes through control of individual cylinder component states.
U.S. Pat. No. 6,223,846 of Michael Schechter describes a method and a system for converting kinetic energy of a vehicle and part of energy supplied by its engine into energy of compressed air to be used to assist in vehicle propulsion later. A system of valves employing variable valve timing and valve deactivation is used to implement and control a two-way flow of compressed air between the engine and an air-reservoir where air-temperature control is maintained. During operation with compressed-air assist the engine operates both as an air-motor and as an internal combustion engine during each cycle in each cylinder. The engine can selectively and interchangeably operate either as a four-stroke or as a two-stroke internal combustion engine.
U.S. Pat. No. 7,231,998 of Michael Schechter is directed to a vehicle engine which has a system of valves that permits various engine cylinders to operate in different modes of operation. During braking, some of the engine cylinders receive atmospheric air, compress it, and transfer it to an intermediate air-container. Other cylinders receive compressed air from the intermediate air-container, further compress it, and transfer it to a high-pressure air-reservoir for storage. During acceleration, some of the engine cylinders receive compressed air from the high-pressure air-reservoir, expand it to a lower level of pressure, and transfer it to the intermediate air-container. Other cylinders receive air from the intermediate air-container, further expand it, and use it for combustion in an internal-combustion cycle. During short stops, the engine is shut down, for the duration of the stop, and, then, it is restarted with compressed air. During cruise, the engine operates as a conventional internal-combustion engine.
FR2836181, assigned to Peugeot Citroen Automobiles SA, describes a combustion engine with several modes of operation. During deceleration and braking valves of one or more cylinders are controlled to make a cylinder work as a compressor delivering compressed gas to a gas reservoir through a flap valve and non return valve combination. The gas stored under pressure is returned to the engine through a plenum and operates to improve engine performance. The connections to the gas reservoir are arranged remotely to the cylinder which significantly reduces the efficiency.
EP1308614, assigned to Peugeot Citroen Automobiles SA, describes a power system which comprises an internal combustion engine with a gas inlet and an exhaust systems. A pressurised gas accumulator is linked to a control unit. The accumulator has an outlet connected through a valve to a turbo compressor which injects gas back into the engine. The intake of the gas accumulator is connected to the engine's exhaust system via a two-way valve connected to the accumulator and the main exhaust pipe, with a non-return valve between the two-way valve and accumulator. Also here all valves related to the charging of the reservoir are arranged outside of the engine cylinder.
U.S. Pat. No. 5,529,549 of David Moyer was published in 1999 and describes a method and an apparatus for improving the fuel economy and reducing emissions of an internal combustion engine by storing compressed air in a reservoir. A computer controls the energy conversion function of the engine by engine and distribution valves which are arranged outside of and remotely to the combustion chamber which results in a reduced efficiency and a limitation of the possible modes of operation. A supercharged engine function is possible by utilizing the compressed air stored in the reservoir.
FR2865769 assigned to the University of Orleans is directed to a process to operate an internal combustion engine in a pneumatic mode. The process involves injecting an additional quantity of air in a combustion chamber during compression phase of the normal cycle of the engine from an air-brake reservoir during the operation of a four-stroke internal combustion engine at low torque. The reservoir is connected to the chamber using a charge valve. The air is injected to obtain the desired engine torque instantaneously. Furthermore the combination of a pneumatic hybrid engine with a turbo compressor is described. The charge valve is actuated by a electromagnetic actuator. The described pump cycle (see FR2865769A1, page 10, line 6 ff) is a purely two stroke cycle with four phases. The described cycles are not of a four-stroke type because no exhaust stroke is present. The engine must therefore be equipped with variable actuators for the intake and exhaust valves such that it becomes possible to switch between two- and four-stroke mode (e.g. it would be necessary to switch-off the exhaust valve to perform the cycle as described). On page 11, line 1 to 5 a four stroke thermal undercharged mode is described.
DE3903474 assigned to AVL Gesellschaft für Verbrennungskraftmaschinenbau describes a method for operating an internal combustion engine in which gas is removed from each cylinder in a predetermined angular range of the crankshaft. The removed gas is fed to a temporary reservoir and is then fed back to the cylinder in another angular range of the crankshaft. The gas is removed from the cylinder after the end of combustion and is then being fed back from the temporary store before the beginning of compression. The target is to the achievement of a variable total charge mass in the combustion chamber while keeping the charge mass of fresh air the same. It is thereby possible to achieve a variable effective compression ratio.
The fuel efficiency of an internal combustion engine can be improved by the well known principle of downsizing the engine. A further approach is based on a combination of pneumatic hybridization with the well-known principle of down-sizing an internal combustion engine. To compensate the loss of power the engine is supercharged by a conventional turbocharger to maintain its peak power. This technology is well established amongst automobile manufacturers. However, one problem immanent to this technology is the so-called turbo-lag during transient engine operation.
One problem of common combustion engines is their low efficiency at part load conditions. To overcome this problem the operating point of the engine can be moved by auxiliary systems in the form of hybrid propulsion systems, e.g. in the form of electric hybrids or pneumatic hybrids. However, all of these attempts have a very complicated setup and therefore tend to be relatively expensive.
A further problem of combustion engines results from the high emissions during cold start. Especially gasoline engines produce a high percentage of their tailpipe emissions during cold start due to the fact that their three way catalytic converter is still cold and therefore cannot convert emissions like CO, NOx and HCs.